The “content” of FIX data is surrounded by session related data, including session-Messages and session-Tags. As a beginner, I was constantly confused over the difference between session-Messages vs session-Tags
A) There are only a few (I guess 5 to 10) session message types, such as heart beat, logon/logout, request for resend…
** All the types — session msg subtypes or app msg subtypes — show up under Tag 35.
B) In ANY (session/app) Message, there are (too many) session-related Tags such as (34)seqNum, (10)checksum, (8)beginString, (9)bodyLength, (52) timeStamp, encryption. I’d say even the all-important (35)MsgType tag qualifies as session tag.
In fact, application data are “surrounded” by session data. App data are the stars of the show, surrounded by a huge “supporting crew” —
– A session msg’s fields are 100% session-related;
– An app msg is not free of session information. It is partly a session msg — due to those session tags.
– If you snoop the conversation, most messages are session messages — heartbeats
– every business data exchange starts with and ends with session messages — logon and logout.